KR102327851B1 - Reflective anode electrode for organic el display - Google Patents

Abstract

The present invention is a reflective anode electrode for an organic EL display, comprising an Al alloy film and an oxide conductive film, and has a laminate structure in which a layer mainly composed of aluminum oxide is interposed at the contact interface between the Al alloy film and the oxide conductive film, The Al alloy film contains Si and a rare earth element, and when the content of Si is a (atomic %) and the total content of the rare earth element is b (atomic %), 0.62 < {a/(a+b) }, 0.2<a<3 and 0.1<b, and wherein the aluminum oxide-based layer contains Si.

Description

Reflective anode electrode for organic EL display {REFLECTIVE ANODE ELECTRODE FOR ORGANIC EL DISPLAY}

The present invention relates to a reflective anode electrode used in an organic EL display (particularly a top emission type). Moreover, it also relates to the sputtering target for forming the thin film transistor substrate and organic electroluminescent display using the said reflective anode electrode, and the Al alloy film contained in the said reflective anode electrode.

An organic electroluminescent (henceforth "organic EL") display is a flat panel display formed by arranging organic electroluminescent elements in matrix form on substrates, such as a glass plate.

Al is also good as a reflective film. For example, Patent Document 1 discloses an Al film or an Al-Nd film as a reflective film, and it is described that an Al-Nd film is preferable because of its excellent reflective efficiency.

However, when the Al film or Al-Nd film is directly contacted with an oxide conductive film such as ITO or IZO as a reflective film, the contact resistance (contact resistance) increases, so that sufficient current can be supplied for hole injection into the organic EL device. none.

Here, Patent Document 2 proposes an Al-Ni alloy film containing 0.1 to 2 atomic% of Ni as a reflective electrode (reflective film) directly connected to the oxide conductive film constituting the transparent electrode. According to this, high reflectance and low contact resistance can be realized.

Further, in Patent Document 3, by using an Al-based alloy film containing 0.1 to 6 atomic% of Ag, as in Patent Document 2, an Al-based alloy reflective film capable of realizing low contact resistance and high reflectance even when in direct contact with an oxide conductive film is provided. has been proposed.

Moreover, in patent document 4, the Al alloy film for display devices containing 0.05-0.5 atomic% of Ge and containing 0.05-0.45 atomic% of Gd and/or La in total is proposed.

Japanese Patent Laid-Open No. 2005-259695 Japanese Patent Laid-Open No. 2008-122941 Japanese Patent Laid-Open No. 2011-108459 Japanese Patent Laid-Open No. 2008-160058

In contrast to the above, in the organic EL display of the top emission type, when an Al alloy is used as the anode electrode, an insulating oxide film is unavoidably formed on the surface of the Al alloy in an oxygen atmosphere. Due to the insulating property of the oxide film, it becomes difficult to flow a current. Therefore, when a current exceeding a predetermined value is attempted to flow, the required voltage value increases. Therefore, power consumption increases when the same light emission intensity is maintained.

The present invention has been made in view of the above circumstances, and it is possible to ensure low contact resistance and high reflectance even when an Al alloy film, which is a reflective film, is in direct contact with an oxide conductive film, and to provide a reflective anode electrode for an organic EL display excellent in heat resistance. The purpose.

In response to the above problem, the present inventors have found that the Al alloy film serving as the reflective film contains a predetermined amount of Si and at least one rare earth element, and the layer containing the oxide interposed at the contact interface between the reflective film and the oxide conductive film also contains Si. , found out that the above problems could be solved, and came to complete the present invention.

That is, the reflective anode electrode for an organic EL display according to the present invention includes an Al alloy film and an oxide conductive film, and a layered structure in which a layer mainly composed of aluminum oxide is interposed at the contact interface between the Al alloy film and the oxide conductive film. wherein the Al alloy film contains Si and at least one rare earth element, and when the Si content is a (atomic %) and the total content of the rare earth elements is b (atomic %), 0.62 < { a/(a+b)}, 0.2<a<3, and 0.1<b are satisfied, and the layer containing aluminum oxide as a main component is characterized in that it contains Si.

In a preferred embodiment of the present invention, the rare earth element contains at least one of Nd and La.

In a preferred embodiment of the present invention, the oxide conductive film has a thickness of 5 to 30 nm.

In a preferred embodiment of the present invention, the Al alloy film is formed by sputtering.

In a preferred embodiment of the present invention, the Al alloy film is electrically connected to the source/drain electrodes of the thin film transistor.

Further, the present invention includes a thin film transistor substrate including any of the above reflective anode electrodes and an organic EL display including the above thin film transistor substrate.

Further, in the present invention, a sputtering target for forming an Al alloy film included in any of the above reflective anode electrodes, wherein the Si content is a (atomic %) and the total content of rare earth elements is b (atomic %), A sputtering target that satisfies the relationships of 0.62<{a/(a+b)}, 0.2<a<3, and 0.1<b is also included.

According to the reflective anode electrode for an organic EL display according to the present invention, the Al alloy film as the reflective film is in direct contact with the oxide conductive film, and even if there is a layer containing aluminum oxide as a main component therebetween, low contact resistance and high reflectance can be ensured. can Moreover, since it is excellent also in heat resistance, it can be set as the thing without surface roughness (hillock).

By using this reflective anode electrode for a thin film transistor substrate and further an organic EL display, current can be efficiently passed through the organic light emitting layer and light emitted from the organic light emitting layer can be efficiently reflected by the reflective film. An organic EL display excellent in luminance can also be realized.

1 is a schematic cross-sectional view showing an example of an organic EL display provided with a reflective anode electrode according to an embodiment of the present invention.
2 : is a figure which shows the Kelvin pattern used for the contact resistance measurement of an Al alloy film and an oxide conductive film.
3 is an EDX spectrum of a layer containing aluminum oxide as a main component during cross-sectional observation by TEM-EDX of the reflective anode electrode of Example 2. FIG.

EMBODIMENT OF THE INVENTION Hereinafter, the form (this embodiment) for implementing this invention is demonstrated in detail. In addition, this invention is not limited to embodiment demonstrated below, In the range which does not deviate from the summary of this invention, WHEREIN: It is a range which can change arbitrarily and can implement.

(organic EL display)

First, the outline of the organic electroluminescent display using the reflective anode electrode of this embodiment is demonstrated using FIG. Note that the Al alloy film used in the present embodiment is an Al-Si-REM alloy film (REM means one or more rare earth elements). Hereinafter, the Al-Si-REM alloy film is simply referred to as an "Al alloy film". is called

A TFT 2 and a passivation film 3 are formed on a substrate 1, and a planarization layer 4 is further formed thereon. A contact hole 5 is formed on the TFT 2 , and the source/drain electrode (not shown) of the TFT 2 is electrically connected to the Al alloy film 6 through the contact hole 5 .

An oxide conductive film 7 is formed directly on the Al alloy film 6 so as to be in contact with the Al alloy film 6 . _{However, in reality, a layer (not shown) containing aluminum oxide (Al 2} O ₃ ) as a main component is formed and interposed at the contact interface between the Al alloy film 6 and the oxide conductive film 7 . In addition, the main component in "the layer which has aluminum oxide as a main component" means the component contained most in a layer, Specifically, it means that it is a component contained 70 mass % or more with respect to the total mass of a layer.

Since Al is very easily oxidized, it is easily combined with oxygen in the atmosphere to easily form a layer containing aluminum oxide on the surface of the Al alloy film. Moreover, when an Al alloy film and an oxide conductive film are brought into contact, Al takes oxygen from an oxide conductive film, and the layer which has aluminum oxide as a main component is easy to form in the contact interface. Since this layer containing aluminum oxide as a main component is insulating, the contact resistance (contact resistance) between the Al alloy film and the oxide conductive film is originally increased.

However, in the present embodiment, by containing a specific amount of Si in the Al alloy film, Si is also contained in the layer mainly composed of aluminum oxide to be formed. At this time, it is presumed that Si exists in the form of bonding of metal bonds in the layer containing aluminum oxide as a main component, and it is thought that low contact resistance between the Al alloy film and the oxide conductive film can be ensured by the presence of this Si. do.

The presence of Si in the layer containing aluminum oxide as a main component is, for example, a transmission electron microscope (TEM) (TEM-EDX) in which XPS (X-ray photoelectron spectroscopy) and EDX (energy dispersive X-ray spectroscopy) analysis are combined. ) can be confirmed by cross-sectional observation of the reflective anode electrode using

Although it is difficult to actually measure the content of Si contained in the layer, in cross-sectional observation of the reflective anode electrode using TEM-EDX, it is preferable that Si be 0.8 atomic% or more.

The Al alloy film 6 and the oxide conductive film 7 act as a reflective electrode of the organic EL element and are electrically connected to the source/drain electrodes of the TFT 2, so that a layer containing aluminum oxide as a main component is formed. The Al alloy film 6 and the oxide conductive film 7 included act as a reflective anode electrode.

An organic light emitting layer 8 is formed on the oxide conductive film 7 , and a cathode electrode 9 is formed thereon.

In such an organic EL display, since the light emitted from the organic light emitting layer 8 is efficiently reflected by the reflective anode electrode of the present embodiment, excellent light emission luminance can be realized. Further, the higher the reflectance of the reflective anode electrode, the better, and the reflectance with respect to light having a wavelength of 450 nm is preferably 79% or more, more preferably 80% or more, and still more preferably 85% or more.

(Al alloy film)

Next, the Al alloy film used for the reflective anode electrode of the present invention will be described.

The Al alloy film contains Si and at least one rare earth element (REM), and their ratio is a case where the content of Si relative to the Al alloy film is a (atomic%) and the total content of REM is b (atomic%). , 0.62<{a/(a+b)}, 0.2<a<3, and 0.1<b are satisfied.

By making a more than 0.2 atomic%, it can be set as the quantity of Si required for ensuring low contact resistance, and it can prevent that a drive voltage becomes high. More than 0.5 atomic% is preferable and, as for a, more than 0.8 atomic% is more preferable.

Moreover, a high reflectance can be maintained by making a into less than 3 atomic%. Less than 2.5 atomic% is preferable and, as for a, less than 1.5 atomic% is more preferable.

By making b more than 0.1 atomic%, generation|occurrence|production of the surface roughness (hillock) generated by the heat history received in a process can be suppressed. Surface roughness causes pixel short circuit. b is preferably 0.2 atomic% or more.

Moreover, although the upper limit of b is limited to the value of a from 0.62<{a/(a+b)}, less than 1 atomic% is preferable and less than 0.5 atomic% is more preferable.

By making the ratio represented by {a/(a+b)} more than 0.62, a low contact resistance can be maintained. This is considered to be because Si and a rare earth element contained in the Al alloy film can be prevented from forming a compound, which makes it difficult for Si concentration to occur in the layer containing aluminum oxide as a main component. More than 0.7 is preferable and, as for ratio represented by {a/(a+b)}, more than 0.8 is more preferable.

In addition, the ratio represented by {a/(a+b)} is preferably less than 0.9 from the viewpoint of ensuring reflectance.

Examples of the rare earth element contained in the Al alloy film include La, Ce, Nd, Sm, Gd, and Tb. Moreover, these elements may add several types of elements simultaneously. Among these, Nd and La are preferable, and it is more preferable that at least either one of Nd and La is included.

The Al alloy film may contain other elements other than Al, Si, and REM within a range that does not impair the effects of the present invention.

As another element, Ge, Cu, Ni, Ta, Ti, Zr etc. are mentioned, for example. 1.0 atomic% or less is preferable with respect to the Al alloy film, and, as for the total content of these other elements and an impurity, 0.7 atomic% or less is more preferable.

The film thickness of the Al alloy film is preferably 50 nm or more, more preferably 100 nm or more, from the viewpoint of ensuring reflectance. Moreover, 300 nm or less is preferable from the point of wiring workability and productivity, and, as for the film thickness of an Al alloy film, 200 nm or less is more preferable.

The Al alloy film is preferably formed by a sputtering method or a vacuum vapor deposition method, and in the sputtering method, forming using a sputtering target (hereinafter sometimes referred to as "target") is excellent in the in-plane uniformity of components and film thickness. It is more preferable at the point that a thin film can be formed easily.

In order to form an Al alloy film by the sputtering method, an Al alloy sputtering target containing the above-mentioned elements (Si and REM) and having the same composition as the desired Al alloy film may be used as the target.

Accordingly, it is a sputtering target for forming an Al alloy film included in the reflective anode electrode, and a sputtering target having the same composition as the Al alloy film is also included within the scope of the present invention.

Specifically, it is a sputtering target for forming an Al alloy film included in the reflective anode electrode, where the Si content is a (atomic %) and the total content of rare earth elements is b (atomic %), 0.62 < { a/(a+b)}, 0.2<a<3, and 0.1<b, it is a sputtering target.

In addition, the composition of a target and the preferable aspect of content represented by a and b are respectively the same as the preferable aspect of the composition and content represented by a and b in the said Al alloy film.

As a method for producing a target, a method for producing and obtaining an ingot containing an Al-based alloy by a melt casting method, a powder sintering method, a spray forming method, etc., or a preform containing an Al-based alloy (an intermediate before obtaining a final compact body) After manufacturing, the method obtained by densifying the said preform by a densification means is mentioned.

The substrate temperature in the sputtering method is preferably 25°C or higher from the viewpoint of suppressing adsorption of moisture and gas on the substrate, and 200°C or lower is preferable, and 150°C or lower is more preferable from the viewpoint of ensuring the surface smoothness of the Al alloy. .

(Oxide Conductive Film)

The oxide conductive film used in the present embodiment is not particularly limited, and commonly used ones such as indium tin oxide (ITO) and indium zinc oxide (IZO) are mentioned. From the viewpoint of low resistance and resistance stability, it is preferably It is indium tin oxide.

5 nm or more is preferable from a viewpoint of preventing that a pinhole generate|occur|produces in an oxide conductive film and becomes a cause of a dark spot, and, as for the film thickness of an oxide conductive film, 10 nm or more is more preferable. On the other hand, from a viewpoint of preventing the fall of the reflectance when it is set as a reflective anode electrode, 30 nm or less is preferable and, as for the film thickness of an oxide conductive film, 20 nm or less is more preferable.

It is preferable to form an oxide conductive film into a film by the sputtering method from the point which can form easily the thin film excellent in the film-plane uniformity of a component and film thickness.

(reflective anode electrode)

In the reflective anode electrode obtained above, in addition to excellent reflectance and low contact resistance, the work function of the oxide transparent conductive film located on the upper layer is controlled to the same degree as when a general-purpose Ag-based alloy is used, and has excellent heat resistance. , used in organic EL displays.

The higher the reflectance of the reflective anode electrode, the better, preferably 79% or more, more preferably 80% or more, and still more preferably 85% or more, with respect to light having a wavelength of 450 nm.

In addition, the low contact resistance means that the contact resistance is preferably 10 kΩ·mm 2 or less, and preferably 2 kΩ·mm 2 , in the measurement by the method described in Examples described later, that is, a four-terminal method using a Kelvin pattern having a contact hole size of 80 × 80 μm. mm2 or less is more preferable.

A reflective anode electrode in which the Al alloy film is electrically connected to the source and drain electrodes of the thin film transistor is also mentioned as a preferred aspect of the present embodiment, and further includes a thin film transistor substrate including a reflective anode electrode, and the thin film transistor substrate The organic EL display to be used is also mentioned as a preferable aspect of this embodiment.

<Example>

Hereinafter, the present invention will be more specifically described with reference to examples, but the present invention is not limited by the following examples, and may be implemented with modifications within a range suitable for the purpose, all of which are It is included in the technical scope of the present invention.

(Fabrication of reflective anode electrode)

An alkali-free glass plate (plate thickness: 0.7 mm) was used as a substrate, and an Al alloy film (film thickness 200 nm) serving as a reflective film was formed on the surface by sputtering. The sputtering conditions were a substrate temperature of 25°C and a pressure of 0.26 Pa, and an Al alloy target was used at 5 to 20 W/cm 2 using a DC power supply. In addition, in the composition of the sputtering target and the Al alloy film formed, the contents (atomic %) of Si, Nd, and La are as shown in Table 1, and the remainder is Al and impurities. This composition was identified by ICP (Inductively Coupled Plasma) emission spectroscopic analysis.

On the Al alloy film obtained above, as an oxide conductive film, an In-Sn-O (Sn: 10 mass%) thin film (ITO thin film) was laminated to a thickness of 10 nm by sputtering. The sputtering conditions were performed at 2 to 4 W/cm 2 using a DC power supply at a substrate temperature of room temperature (about 25° C.) and a pressure of 0.26 Pa.

Thereafter, heat treatment (post annealing) was performed by holding at 250° C. for 1 hour in a nitrogen atmosphere to prepare a reflective anode electrode.

(Identification of a layer containing aluminum oxide as a main component)

With respect to the obtained reflective anode electrode, a layer containing aluminum oxide as a main component exists between the Al alloy film and the oxide conductive film by XPS (X-ray photoelectron spectroscopy), and Si is contained in the layer as a bonded state of a metal bond. confirmed that there is.

In addition, a transmission electron microscope (TEM-EDX) combined with energy dispersive X-ray spectroscopy (TEM observation apparatus: JEM-2010F field emission transmission electron microscope manufactured by Nippon Electronics Co., Ltd., acquisition camera: CCD UltraScan manufactured by Gatan, EDX analysis apparatus: Cross-sectional observation of the reflective anode electrode was performed using JED-2300T SDD made by Nippon Electronics (JEM-2010F attached)) under the conditions of an acceleration voltage of 200 kV and a beam diameter (EDX analysis) of about 1 nm in diameter. For example, with respect to the reflective anode electrode of Example 2, cross-sectional observation was performed at four locations with a depth of 5 nm, 12 nm, 15 nm and 40 nm from the electrode surface (upper layer side), and from the obtained TEM image and EDX spectrum, each oxidation It was confirmed that the conductive film, the layer containing aluminum oxide as a main component, the Al alloy film, and the Al alloy film correspond to each other.

The EDX spectrum of the layer which has aluminum oxide as a main component in Example 2 is shown in FIG. From Fig. 3, it can be seen from the peaks of Al and O and their contents (atomic%, at%) that it is a spectrum of a layer containing aluminum oxide as a main component. The peak of Si was also confirmed in the said layer, and the content was 2.5 atomic%.

(reflectivity)

With respect to the reflective anode electrode (after heat treatment), using a visible/ultraviolet spectrophotometer "V-570" manufactured by Nippon Bunko Co., Ltd., the spectral reflectance in the range of measurement wavelength: 1000 to 250 nm was measured. Specifically, a value obtained by measuring the reflected light intensity of the sample with respect to the reflected light intensity of the reference mirror was defined as "reflectance". Although the reflectance in measurement wavelength 450nm is shown in Table 1, the said reflectance is favorable in it being 79 % or more, and it was set as the pass.

(Heat resistance)

Evaluation of the heat resistance of the reflective anode electrode (after heat treatment) was performed by observing the surface with an optical microscope and confirming the presence or absence of irregularities (surface roughness, hillock) at a magnification of 1000 times. Specifically, within an arbitrary range of 140 x 100 µm, those with less than 5 hillocks with a diameter of 1 µm or larger are judged as "no hillock", and good (○), and those with 5 or more hillocks are classified as "hillock oil". It judged and it was set as defective (x).

In addition, as the heat resistance of the reflective anode electrode, observation by a differential interference microscope was also performed on the electrode surface after heat treatment to confirm the presence or absence of surface roughness (hillock). As a result, it was confirmed that all of the reflective anode electrodes judged to be good (circle) by surface observation with the optical microscope were smooth surfaces.

(contact resistance)

The Kelvin pattern shown in FIG. 2 was used for the contact resistance (contact resistance) of an Al alloy film and an oxide conductive film. After the Kelvin pattern is formed by forming the Al alloy film, 10 nm of an In-Sn-O (Sn: 10% by mass) thin film as an oxide conductive film is subsequently laminated to form a wiring pattern, and then a SiN passivation film is formed on the surface of the Kelvin pattern. A film (film thickness: 200 nm) was formed by a plasma CVD (chemical vapor deposition) apparatus.

Film formation conditions were substrate temperature: 280°C, gas ratio: SiH ₄ /NH ₃ /N ₂ =125/6/185, pressure: 137 Pa, and RF power: 100 W.

After the SiN film formed was patterned, a Mo film (film thickness: 300 nm) was formed on the surface by sputtering, and further, the Kelvin pattern of Fig. 2 was obtained by patterning the formed Mo film.

The measurement method of contact resistance is to produce a Kelvin pattern (contact hole size: a square with one side of 80 µm) shown in Fig. 2, and measure four terminals (a current is passed through an Al alloy \ITO laminated film, and an Al alloy is used at a separate terminal) A method of measuring the voltage drop between the \ITO stacked films) was performed. Specifically, by passing a current I between _{I 1} -I _{2 in} FIG. 2 _{and monitoring the voltage V between V 1} -V ₂ , the resistance R of the contact portion _{is changed to [R=(V 1} -V ₂ )/I _{2 ).} ] was obtained. A value obtained by multiplying the resistance R by the area of the contact portion and converting the area resistance (Ω·mm 2 ) into the contact resistance was preferably 10 kΩ·mm 2 or less (10000 Ω·mm 2 or less) and passed.

The composition and evaluation results of the Al alloy film of the obtained reflective anode electrode are collectively shown in Table 1. In addition, with comprehensive evaluation, the case where all of the said reflectance, heat resistance, and contact resistance were made into (circle) was made into (circle), and the case where even one was inferior was made into *. In addition, {a/(a+b)} in an Al alloy film is shown as {Si/(Si+REM)} in a table|surface.

From the above, by including Si in the Al alloy film, it was confirmed that Si was also contained in the layer mainly composed of aluminum oxide interposed between the Al alloy film and the oxide conductive film. When the content of Si and rare earth elements contained in the Al alloy film is set to 0.62<{Si/(Si+REM)}, 0.2<Si<3 and 0.1<REM, low contact resistance and high reflectance with respect to the reflective anode electrode obtained and good heat resistance was confirmed.

Although this invention was detailed also demonstrated with reference to the specific embodiment, it is clear for those skilled in the art that various changes and correction can be added without deviating from the mind and range of this invention.

This application is based on Japanese Patent Application No. 2019-101560 for which it applied on May 30, 2019, The content is taken in here as a reference.

1: substrate
2: TFT
3: passivation film
4: planarization layer
5: contact hole
6: Al alloy film
7: oxide conductive film
8: organic light emitting layer
9: cathode electrode

Claims (9)

A reflective anode electrode for an organic EL display,
It includes an Al alloy film and an oxide conductive film, and has a laminated structure in which a layer containing 70 mass % or more of aluminum oxide is interposed at the contact interface between the Al alloy film and the oxide conductive film,
The Al alloy film contains Si and at least one rare earth element, and when the Si content is a (atomic %) and the total content of the rare earth elements is b (atomic %), 0.62 < {a/ (a+b)}, 0.2<a<3 and 0.1<b, and
The reflective anode electrode, wherein the layer containing 70% by mass or more of aluminum oxide includes Si. According to claim 1,
The reflective anode electrode, wherein the rare earth element contains at least one of Nd and La. According to claim 1,
The reflective anode electrode, wherein the oxide conductive film has a thickness of 5 to 30 nm. 3. The method of claim 2,
The reflective anode electrode, wherein the oxide conductive film has a thickness of 5 to 30 nm. 5. The method according to any one of claims 1 to 4,
A reflective anode electrode, wherein the Al alloy film is formed by a sputtering method. 5. The method according to any one of claims 1 to 4,
The reflective anode electrode, wherein the Al alloy film is electrically connected to the source/drain electrodes of the thin film transistor. A thin film transistor substrate comprising the reflective anode electrode according to any one of claims 1 to 4. An organic EL display comprising the thin film transistor substrate according to claim 7 . A sputtering target for forming an Al alloy film contained in the reflective anode electrode according to any one of claims 1 to 4,
Assuming that the Si content is a (atomic%) and the total content of rare earth elements is b (atomic%), the relationships of 0.62<{a/(a+b)}, 0.2<a<3, and 0.1<b A sputtering target that satisfies.

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